The present invention relates to a compressible stop member for use on a crane, such as a boom stop used on a mobile lifting crane, and particularly a compressible stop member that includes an accumulator.
Lift cranes typically include a carbody; ground engaging members elevating the carbody off the ground; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; and a boom pivotally mounted on the rotating bed, with a load hoist line extending there from. For mobile lift cranes, the ground engaging members are moveable ground engaging members. There are different types of moveable ground engaging members, most notably tires for truck mounted cranes, and crawlers. Typically the mobile lift cranes include a counterweight to help balance the crane when the crane lifts a load.
A crane with a povitable boom will typically include a compressible stop member, often referred to as a boom stop, used to prevent the boom from tipping over backwards, particularly if a load is suddenly released while the boom is at a steep boom angle. Known boom stops typically included a spring so that the boom stop can start to engage the boom as it is moving to a steep boom angle but before it reaches a point where it would tip backward. The spring applies greater and greater force the further the boom stop is compressed. This compression provides a return force to push the boom back to conventional working angles when the reason it was raised so steeply has ended. A conventional boom stop might be built with a tube inside of a tube, with a spring inside of the tubes. If the boom came into contact with the boom stop and still continued to travel to where it might tip over backward, the spring would be compressed until it reached a solid height, thus greatly increasing the stopping ability of the boom stop.
While such boom stops have proven themselves to be adequate, they have a disadvantage in that the spring and tube arrangement cannot be easily scaled up in size due to physical limitations on the space available for the boom stop. For example, a larger crane that has higher capacities may not necessarily be proportionately larger in all dimensions. The larger crane will need a boom stop that can absorb more energy, but the space in which to deploy that boom stop may not be large enough that a larger spring and tube arrangement can simply be used for the boom stop. Thus there remains a need for a boom stop that can generate greater stopping force in a more compact space.
Some cranes also include a luffing jib. The luffing jib usually includes a jib stop, used to also prevent the jib from tipping over backward at high jib angles. The same issues discussed above with respect to boom stops are often applicable to jib stops. Some cranes also include a mast, and struts such as jib struts. The present invention may also be useful for compressible stop members used for these other crane columns.